The invention relates to a socket for accommodating a head and/or an insert for insertion into a head of a fastener to be set and for holding the fastener as well as for driving the fastener during a setting process, wherein the socket and/or insert is provided with a plurality of jaws, which are disposed in succession in circumferential direction and which engage in a tubular holder, in which they are locked against rotation but can slide axially relative thereto between two end positions.
In the very act of setting self-tapping screws, relatively long boring times are repeatedly encountered due to the fact that appropriately high pressing pressure cannot be exerted in advance, since there exists a risk that the screw will tilt in the socket and/or insert, because on the one hand the screw heads have large manufacturing-related tolerances and because on the other hand the boring point slips along the workpiece. Under some circumstances a screw must be started repeatedly until the point of the boring part engages, especially on a smooth metal surface. Only then can full pressure be exerted on the driving device, and so the necessary boring pressure is available only from that instant on.
In the use of commercial sockets for setting fasteners, especially self-tapping fasteners, relatively long boring times are encountered in the case of one-hand operation merely because of the fact that the point of the boring part slips repeatedly, because otherwise there exists the risk that the fastener will tilt. If only light pressure can be exerted, on the other hand, the risk that the point will slip becomes substantially greater.
A socket with the features listed in the preamble of claim 1 is known from U.S. Pat. No. 4,213,355. This socket cannot be operated with one hand in order to clamp a fastener such as a screw in such a way that it is certain that the risk of tilting of the fastener from the socket during a setting process can be prevented from the very beginning. To clamp a nut, for which the known socket is mainly designed, a ratchet wrench must be held with one hand and an adjusting piece on the socket must be turned with the other hand, until the nut introduced beforehand between jaws is firmly clamped in the jaws. Thus one-hand operation becomes possible once the nut has initially been firmly clamped using both hands.
This is due to the fact that this known socket is constructed like a drill chuck, in which a sleeve must also be turned relative to the jaw holder in order to execute a clamping process. To clamp a screw, it would be additionally necessary to proceed very carefully and to exert considerable force in order to be certain that the risk of tilting from the socket during a setting process will be avoided from the very beginning.
From German Patent 847429 there is known a working head for power-operated screwdrivers for screwing stud bolts or stud screws into blind holes. The working head comprises two clamping jaws which are accommodated in a drive sleeve where they are axially slidable but locked against rotation and whose faces turned toward each other roll over each other to change the clamping faces from an open position to the closed position thereof, a front abutment which is allocated to the two clamping jaws, has the form of a first ball and is provided for a stud bolt to be accommodated and, on the sleeve, an end abutment which has the form of a second ball and which passes between the rear ends of the clamping jaws during their axial displacement by the stud bolt impinging on the front abutment and spreads them to close the clamping ends. The clamping ends are provided with internal threads and are open in a lower home position. When a stud bolt or the like is inserted into the working head, it presses the first ball upward into contact with the clamping jaws, which are thus pushed upward and are spread upwardly apart by the second ball. The clamping jaws thus swivel around the point of contact with the first ball, so that the clamping ends close downwardly around the stud bolt. The threaded engagement between clamping jaws and stud bolt allows for a certain tolerance without impairing the clamping process. However, if the clamping ends have internally smooth faces for clamping a fastener head, for example, clamping over an area would be possible only for a very well defined head size. In the event of any manufacturing-related deviation of the fastener head, only line contact would exist between this head and the clamping ends because of the pincer-like closing process of the clamping jaws, and this would not be sufficient to clamp such a fastener so firmly that it could not tilt during a setting process in which boring would have to take place.
The object of the invention is to provide a socket and/or insert of the type indicated in the preamble of claim 1, with which socket and/or insert a fastener can be gripped so simply and securely that the risk of tilting of the fastener from the socket and/or insert during a setting process is prevented from the very beginning.
This object is achieved according to the invention by the fact that, for accommodating a head and/or for insertion into a head, the jaws in their one end position can be forced apart or squeezed together in radial direction by the head, and the jaws, during application thereon of axial force directed toward the other end position, are necessarily squeezed together or forced apart in radial direction by mutual action between holder and jaws, and that, on the inside of the holder and/or on the outside surface of the jaws there are formed camming faces running taperingly relative to the central axis, and so the jaws can be squeezed toward each other by virtue of the camming faces during axial insertion into the holder.
In the socket and/or insert according to the invention, the jaws are moved parallel to each other during the clamping process. Regardless of possible tolerances in the dimensions of a fastener head, this is therefore always clamped over areas extending the entire head length and parallel to the axis thereof, the firmness of such clamping increasing with magnitude of the axially exerted force. When appropriate full pressure is exerted on the driving tool during starting of the fastener or of the boring part of the fastener on a substructure, the jaws move into their holder due to this application of axial force and therein are necessarily squeezed together in radial direction by virtue of special interlocking structures, so that the screw head is firmly clamped in vise-like manner. Thus, as long as appropriate full pressure is exerted by the driving tool on the fastener, the fastener head remains firmly clamped, and so on the one hand tilting of the fastener in the socket and/or insert is precluded and on the other hand it is ensured by the firm clamping action that the point of a boring part of a fastener penetrates directly at the started region without any slipping of the point. Thus the hole is always bored at the desired location.
Because of the excellent clamping of the screw head in the socket and/or insert and the fact that the point of the boring part of the fastener is thereby guided correctly, the full pressure can be applied from the very beginning.
It has even been shown in experiments that boring and driving of a screw oriented at an acute angle to the workpiece surface is also possible if necessary without slipping of the point of the boring part. The point of the boring part penetrates immediately into the workpiece directly at the started position precisely because full pressure can be applied from the very beginning.
By means of the camming faces, which run taperingly relative to the central axis on the inside of the holder and/or on the outside surface of the jaws, the jaws can be squeezed against each other by virtue of the camming faces during axial insertion into the holder, and a correspondingly amplified radial force is already exerted on the fastener head without application of excessive axial force, so that the fastener head is firmly clamped immediately after the point of the boring part of the fastener has been started. Thus, by means of the tapered camming face, there is achieved appropriate force amplification, by which optimal clamping and also appropriate axial alignment between the axis of rotation of the driving tool and the central axis of the fastener are produced.
In this connection, it is expedient for tapered camming faces to be provided both on the holder and on the jaws. Because the camming faces are designed to correspond to each other, they can bear on each other over a relatively large area and thus optimum force transfer is also achieved during axial insertion of the jaws into the holder.
In one advantageous embodiment, the jaws are squeezed together in radial direction under spring loading. Consequently the jaws remain in their rest position, or in other words bearing against each other even when not forcibly squeezed together, so that they are forced apart resiliently during insertion of the fastener head. Thereby it is guaranteed that the fastener head will at first be held in the socket and/or insert by the spring action alone, and so even fasteners directed downward can be set without problems, because the fastener will be held sufficiently firmly by the resilient structure of the jaws. To set the fastener, and thus during the boring process, appropriate axial pressure is exerted, so that the action of the camming faces begins only then and the fastener head is necessarily clamped between the jaws of the socket and/or insert.
It is further proposed that the jaws forming the socket and/or insert are spring-loaded axially outward from the holder. Thereby it is ensured that the jaws always release and return to their rest position after the end of a driving process.
A simple alternative embodiment provides that the jaws are squeezed resiliently toward each other by an O-ring placed in a groove on the outer circumference of the jaws.
When it is further proposed that the groove for accommodating the O-ring be formed in the region of the tapered camming face, then a geometry which is structurally very simple and effective can be created. The region which inherently flares conically already because of the tapered camming faces is utilized appropriately, since here the relatively largest material thickness is available for making such a groove. Moreover, the additional advantage is obtained thereby that the inserted O-ring acts precisely in that region in which it is desired, namely in that region in which the fastener head is held between the jaws.
In the embodiment in which the jaws have the form of circular sectors and together form a cylindrical structural member on the whole, the advantage is obtained that a kind of encircling truncated cone can be formed both in the holder and in the socket and/or insert or jaws of the socket and/or insert, so that radial forces act all around on the jaws when the socket and/or insert is pushed axially into the holder.
In order that sticking or jamming of the socket and/or insert in the holder itself cannot occur, it is provided in a simple structural embodiment that a circumferential groove is formed at the transition between the tapered camming face on the holder and the accommodating region in which the jaws are fixed to be driven in rotation therewith. This guarantees that only the tapered camming faces of the holder and of the jaws are braced against each other at all times, and that these tapered camming faces of the jaws can never penetrate into the accommodating region disposed therebehind in which the jaws are fixed to be driven in rotation therewith.
According to a special embodiment, it is provided that the jaws together form a kind of pot-like socket and/or insert, wherein webs projecting toward the central axis at the end of the jaws facing away from the accommodation for the fastener head form a stop for the head of a fastening screw, the head limiting the axial movability of the socket and/or insert formed from the jaws. Inherently there is needed only a very short distance of relative positionability between the socket and/or insert and the holder in order to have the capability of inserting the fastener head and in order to clamp the fastener head optimally during starting of the point of the boring part of the fastener. Under certain circumstances an axial movability of 1 to 2 mm is sufficient on the one hand for the jaws to be disposed in a sufficiently loose position and on the other hand for proper bracing to be achieved.
A further advantage is obtained from the small axial movability, in that the O-ring inserted at the outside circumference of the jaws is covered by the holder itself when the jaws are in assembled position. Thus the O-ring is also held captively. By virtue of the arrangement of a fastening screw, a very simple structural geometry is inherently obtained for the holder of the jaws forming the socket and/or insert, wherein the additional advantage is achieved that the arrangement according to the invention plus the socket and/or insert is not substantially larger than a commercial socket and/or insert for inserting and driving fasteners.
So that exact loosening of the jaws of the socket and/or insert is always ensured, meaning that, after completion of the boring or screwing process, the socket and/or insert returns to the starting position in which the screw head can be extracted from the socket and/or insert and in which the jaws of the socket and/or insert can be forced radially outward, it is expedient to provide, encircling the fastening screw between holder and socket and/or insert, a spring such as a stack of cup springs, a helical spring, a spring lock washer or the like to provide axial spring loading of the jaws. In this way it is possible to select a structural geometry which nevertheless ensures a very small construction.